Safety switch for preventing voltages below a predetermined value in a circuit



y 1966 T. N. BRYLA ETAL 3,262,389

SAFETY SWITCH FOR PREVENTING VOLTAGES BELOW A PREDETERMINED VALVE IN A CIRCUIT Filed Feb. 20, 1964 SOURCE AND STORAGE OF ENERGY INVENTORS THEODORE N. BRYLA FLOYD E. JACKS BY ROBERT M. HILLYEIR ATTORNEY United States Patent SAFETY SWITCH FOR PREVENTING VOLTAGES This invention generally relates to a voltage control switch, and more particularly to a safety switch for holding an electric circuit open to prevent voltages accidentally occurring in electrical conductors or other components of the electric circuit from inadvertently actuating a mechanism associated with the electric circuit.

Under certain conditions, it is desired to store electrical energy until the voltage thereof increases to a selected value. When the voltage reaches the selected value, it may be discharged from the source for whatever purposes desired, such as the ignition or detonation of explosive materials which may require the sudden application of a very high voltage. The occurrence of accidental volt-' ages in an electric detonating circuit for an explosive material may result in premature detonation of the explosive materiaL. Heretofore, a gap switch comprising a pair of spaced apart electrodes with air or an inert gas introduced as a dielectric in the space between the electrodes in a hermetically sealed compartment has been disposed in an electric circuit to hold the circuit open until voltage of a selected value is obtained and discharged through the circuit. When the applied voltage reached a predetermined magnitude, the gas serving as a dielectric between the electrodes became ionized so that electric current could flow through the ionized gas between the electrodes to complete the electric circuit. This type of voltage control switch is not reliable, however, when subjected to temperature gradients between 65 F. and 350 F. because the dielectric substance has a tendency to adversely affect the voltage breakdown characteristics of the switch under such temperature conditions. If the voltage breakdown characteristics of this switch are adversely affected, it may fail to hold the electric circuit open when a voltage of less than the predetermined value occurs in the circuit, and inadvertent detonation of the explosive material may result.

It is therefore, an object of this invention to provide an improved voltage control switch which can be relied upon to hold an electric circuit open until a selected predetermined voltage is obtained and discharged through the circuit even though the switch may be subjected to a temperature gradient of significant magnitude.

It is another object of this invention to provide an improved voltage control switch comprising a pair of spaced apart terminals and an intermediate plug of electrically conductive material provided with a dielectric coating, wherein the plug is interposed between the terminals so that the switch remains openuntil a selected predetermined voltage of a magnitude sufiicient to break down the dielectric coating on the plug is obtained for discharge through the switch and the circuit. The plug of electrically conductive material with the dielectric coating is substantially unaffected by temperature changes, and unlike the substances employed as dielectrics in voltage control switches heretofore known will not adversely affect the voltage breakdown characteristics of the switch when the switch is subjected to temperature gradients of significant magnitude.

Certain objects of the invention having been stated, other objects will become apparent as the invention is better understood from the following specification and the accompanying drawings, in which:

3,262,389 Patented July 26, 1966 FIGURE 1 is a longitudinal sectional view of a voltage control switch constructed in accordance with the present invention;

FIGURE 2 is an end elevational view taken along line 2-2 of FIGURE 1 and looking in the direction of the arrows; and t FIGURE 3 is an end elevational view taken along line 3-3 of FIGURE 1 and looking in the direction of the arrows.

Referring more specifically to FIGURE 1 of the drawings, a voltage control switch constructed in accordance with the present invention is generally designated by the reference numeral 12. The switch 12 comprises a housing 14 which may be metallic, the housing 14 having a centrally disposed cylindrical bore 16. The opposite ends of the bore 16 are partially restricted by annular walls 17, 19 which extend radially inwardly from the housing 16. Each of the annular walls 17, 19 comprises a radially inner cylindrical sleeve 18 of electrically conductive material, such as a suitable metal, a radially outer cylindrical sleeve 20 of insulating material, such as glass, fixedly secured about the inner electrically conductive sleeve 18, and a layer of suitable adhesive material 22 bonding the insulating sleeve 20 to the bore-defining surface of the housing 14. The annular walls 17, 19 are axially spaced apart in the housing 14, and the inner electrically conductive sleeves 18 thereof provide respective elongated openings 24 therethrough for receiving terminal members 26, 28 of the switch 12. Each of the terminal members 26, 28 comprises a cylindrical terminal plug of electrically conductive material which is pressed into its respective opening 24 so as to be :frictionally secured within the electrically conductive sleeve 18 corresponding thereto in axially spaced relation to the other terminal plug.

It will be seen that the terminal plugs 26, 28 serve as closures for the openings 24 in the annular walls 17, 19 so as to provide a central cavity or compartment 30 in the housing 14 between the annular walls 17, 19. In accordance with the present invention, a bridging element or connector member 32 is mounted in the compartment 30 so as to extend axially between the annular walls 17, 19, the opposite ends of the connector member 32 being respectively received within the openings 24 at the proximally related ends thereof. The connector member 32 comprises a cylindrical connector plug of electrically conductive material having a dielectric coating or shell covering its entire outer surface area. The. opposite ends of the connector plug 32 are pressed into the proximal ends of the openings 24 to frictionally secure the connector plug 32 between the electrically conductive sleeves 18, 18.

It is preferred that the connector plug 32 be formed of an inorganic electrically conductive material, such as aluminum, having an outer dielectric coating or shell of an inorganic dielectric material, such as aluminum oxide. Such a connector plug 32 is not subject to deterioration to any appreciable degree even when environmental conditions may be severe.

A bridge wire or detonator 34 is secured to the terminal plug 28 and the housing 14. An explosive charge 36 in the form of a metal oxidant or an explosive material is disposed in a counterbore 38 providing a recess or receptacle in one end of the housing 14. The bridge wire or detonator 34 extends across a portion of the explosive charge 36 in engagement therewith.

The terminal plug 26 extends outwardly of the respective opening 24 in which it is received, and its outer end is connected to one end of an electrical conductor or wire 40 leading to a source-and storage of electrical energy 44 to which the other end of the wire 40 is connected. An electrical conductor or wire 42 completes the components of the electric circuit, the wire 42 being connected between the source and storage of electrical energy 44 and the housing 14.

It will be understood that the electric circuit is normally held open by the switch 12 because of the dielectric coating or shell forming the exterior surface of the connector plug 32. Thus, the energy potential in the source and storage of electrical energy .44 can be increased without causing voltage to be discharged through the circuit because of the dielectric coating or shell on the connector plug 32. When the energy potential in the source and storage of electrical energy 44 is increased to a voltageo'f a selected predetermined amount, however, the dielectric coating or shell on the connector plug 32 breaks down and voltage of the selected predetermined magnitude" passes" from the source and storage. of electrical energy 44 through the wire 40, through terminal plug 26, across the electrically conductive sleeve 18 of wall 17, through the electrically conductive body of the connector plug 32, across the electrically conductive sleeve 18 of wall 19, through terminal plug 28, and across bridge wire or detonator 34. This discharge of voltage at a selected predetermined magnitude through the electric circuit explodes or detonates the bridge wire or deton-ator 34 to cause the explosive charge 36 to be detonated.

The magnitude of the voltage necessary to break down the dielectric coating or shell on the connector plug 32 for causing voltage to be discharged through the electric circuit is determined by the thickness and the characteristics of the dielectric coating or shell on the connector plug 32. Generally, as the dielectric coating or shell increases in thickness, its ability to withstand voltage breakdown also increases so that the minimum voltage required to break down the dielectric coating or shell must be of a higher magnitude. Although aluminum oxide is to be preferred as a dielectric material covering the body of the connector plug 32 because of its excellent dielectric characteristics and its ability to remain unaffected when subjected to various environmental conditions, such as being exposed to X-rays, other suitable dielectric materials may be employed as an outer covering for the body of the connector plug 32.

It will therefore be seen that we have disclosed a voltage control switch of improved reliability which prohibits the completion of an electric circuit in which it is disposed, thereby preventing transient voltages lower than a predetermined magnitude from being discharged through the circuit, until voltage of the predetermined magnitude is obtained whereupon the voltage of predetermined magnitude is discharged across the switch and through the conduit.

While the foregoing is a description of a preferred embodiment of the invention, it is to be understood that the same is susceptible of further changes, modifications, and improvements coming within the scope of the appended claims.

We claim:

1. A switch mechanism comprising (a) a pair of spaced electrically conductive cylindrical sleeves,

(b) a pair of spaced cylindrical electrical terminal plugs respectively received in the distal ends of said electrically conductive sleeves in electrical contact therewith,

(c) each of said terminal plugs being adapted to be connected across a source of electric energy,

(d) a cylindrical connector plug interposed between said pair of spaced electrically conductive sleeves and having its opposite ends fiictionally received within the proximal ends of said electrically conductive sleeves, v

(e) said connector plug comprising a body of electrically conductive material at least partially covered by a dielectric material,

(f) said dielectric material on said connector plug covering the surf-aces of the end portions of said connector plug in respective engagement with said pair of spaced electrically conductive sleeves to prevent inadvertent discharge of voltage across the space therebetween bridged by said connector plug, and

(g) said dielectric material being broken down by a predetermined -voltage. magnitude for. discharging, a...

selected voltage of the predetermined magnitude across the space between said pair of electrically conductive sleeves through the electrically conductive body of said connector plug.

2. In an electric detonating circuit having a switch mechanism for controlling the completion of the electric detonating circuit, said switch mechanism comprising (a) a housing,

(b) a pair of axially spaced electrically conductive cylindrical sleeves mounted in said housing,

(c) a pair of spaced cylindrical electrical terminal plugs respectively received in the distal ends of said electrically conductive sleeves in electrical contact therewith,

(d) an axially extending electrically conductive cylindrical connector plug having its outer surface at least partially covered by a dielectric material,

(c) said connector plug being interposed between said pair of spaced electrically conductive sleeves and having respective outer surface portions covered by dielectric material on its opposite ends trictionally received within the proximal ends of said electrically conductive sleeves to prevent inadvertent discharge of voltage across the space therebetween bridged by saidconnector plug,

(f) an explosive charge carried by said housing and disposed adjacent to one of said terminal plugs,

(g) said dielectric material on said connector plug being broken down by a predetermined voltage magnitude for discharging a selected voltage of the predetermined magnitude across the space between said pair of electrically conductive sleeves through the electrically conductive connector plug, and

(h) said explosive charge being detonated in response to the discharge of voltage across the space between said pair of electrically conductive sleeves through the electrically conductive connector plug.

References Cited by the Examiner UNITED STATES PATENTS 2,953,720 9/ 1960 Engel 315--209 3,117,519 1/1964 Hamilton et al. 102-28 3,120,182 2/1964 Chessin et a1 10228 FOREIGN PATENTS 960,186 6/ 1964 Great Britain.

BENJAMIN A. BORCHELT, Primary Examiner.

R. V. LOTTMANN, Assistant Examiner. M 

1. A SWITCH MECHANISM COMPRISING (A) A PAIR OF SPACED ELECTRICALLY CONDUCTIVE CYLINDRIDRICAL SLEEVES, (B) A PAIR OF SPACED CYLINDRICAL ELECTRICAL TERMINAL PLUGS RESPECTIVELY RECEIVED IN THE DISTAL ENDS OF SAID ELECTRICALLY CONDUCTIVE SLEEVES IN ELECTRICAL CONTACT THEREWITH, (C) EACH OF SAID TERMINAL PLUGS BEING ADAPTED TO BE CONNECTED ACROSS A SOURCE OF ELECTRIC ENERGY, (D) A CYLINDRICAL CONNECTOR PLUG INTERPOSED BETWEEN SAID PAIR OF SPACED ELECTRICALLY CONDUCTIVE SLEEVES AND HAVING ITS OPPOSITE ENDS FRICTIONALLY RECEIVED WITHIN THE PROXIMAL END OF SAID ELECTRICALLY CONDUCTIVE SLEEVES, (E) SAID CONNECTOR PLUG COMPRISING A BODY OF ELECTRICALLY CONDUCTIVE MATERIAL AT LEAST PARTIALLY COVERED BY A DIELECTRIC MATERIAL, (F) SAID DIELECTRIC MATERIAL ON SAID CONNECTOR PLUG COVERING THE SURFACES OF THE END PORTIONS OF SAID CONNETOR PLUG IN RESPECTIVE ENGAGEMENT WITH SAID PAIR OF SPACED ELECTRICALLY CONDUCTIVE SLEEVES TO PREVENT INADVERTENT DISCHARGE OF VOLTAGE ACROSS THE SPACE THEREBETWEEN BRIDGED BY SAID CONNECTOR PLUG, AND (G) SAID DIELECTRIC MATERIAL BEING BROKEN DOWN BY A PREDETERMINED VOLTAGE MAGNITUDE FOR DISCHARGING A SELECTED VOLTAGE OF THE PREDETERMINED MAGNITUDE ACROSS THE SPACE BETWEEN SAID PAIR OF ELECTRICALLY CONDUCTIVE SLEEVES THROUGH THE ELECTRICALLY CONDUCTIVE BODY OF SAID CONNECTOR PLUG. 